Evaluation of varying ductile fracture criterion for 7075 aluminum alloy

As one of the principal failures, ductile fracturing restricts metal forming process. Cockcroft-Latham type fracture criterion is suited for ductile fracture in bulk metal-forming simulation. Finding a way to evaluate the ductile fracture criterion (DFC) and identify the relationship between DFC and deformation conditions for a strain-softening material, 7075 aluminum alloy; however, it is a non-trivial issue that still needs to be addressed in a greater depth. An innovative approach is brought forth that the compression tests and numerical simulations provide mutual support to evaluate the ductile damage cumulating process and determine the DFC diagram. One of the results shows that for a fixed temperature, the maximum cumulated damage decreases regularly with increasing strain rate. The most important result shows that DFC of 7075 aluminum alloy at temperatures of 573–723 K and strain rates of 0.01-10 s−1 is not a constant but a change in a range of 0.255-0.453, thus it has been defined with varying ductile fracture criterion (VDFC) and characterized by a function of strain rate and temperature. According to VDFC diagram, the exact fracture moment and position during various forming processes will be predicted conveniently, in addition to which, the deformation domains with lower fracture risk corresponding to higher VDFC can be identified.